1. Field of the Invention
The present invention generally relates to metal forming machinery and more specifically, to an apparatus for making a continuous helically wound flexible pipe with an interlocked metal strip.
2. Description of the Prior Art
Flexible pipes made by shaping a metal strip and interlocking it on a mandrel have been made for many years and are used in a variety of applications including the use of such flexible structures as support members for the manufacture of flexible tubular pipes and conduits having high mechanical strength characteristics. These products, with high resistance to internal and external pressures, have been increasingly used for the transportion of fluids in situations where rigid steel pipes cannot be used or are economically too expensive.
Interlocked flexible pipes in short lengths are also used in a variety of applications like automotive exhaust connections, armouring of electrical cables, conduits, etc.
Equipment for manufacturing spiral pipes or helically interlocked tubing, have been known and used at least as early as 1876. Such equipment falls into one of two general categories: stationary or rotating machines.
Stationary machines normally include a supply reel, forming rollers, a mandrel and pressure rollers to wind the preformed strip over the mandrel. In this solution the machine is stationary while the pipe that is being made rotates about its longitudinal axis. The mandrel can be stationary or rotating in the direction of the moving strip.
The prior art shows examples of all possible solutions from fixed mandrel to mandrel overdriven in relation to the product to be formed. This prior art is clearly shown in U.S. Pat. Nos. 183,328, 2,162,355, 3,515,038 and 2,693,779.
It is clear that with stationary machines there is a limitation to the length that can be produced because of the necessity to rotate the product limits the length that can be economically made with this type of equipment. Long lengths can only be made if a rotatable takeup system is added and such equipment is very expensive when one thinks that a takeup reel for this product is tens of feet in diameter.
Furthermore, the rotation of the takeup equipment must be synchronized with the rotating product and in view of the large masses involved, the speed of rotation of the reel and therefore the productivity of such a system is very low.
In order to overcome such difficulties, rotating machines, such as the ones known from British Pat. No. 110,576, U.S. Pat. Nos. 1,703,250, 1,703,251 and 4,597,276 and French Patent No. 985,067 were developed. These apparatuses normally include a circular plate which turns around a horizontal axis coincident with the longitudinal axis of the tubular structure to be formed. The plate, frame or other rotating member turn around the axis of the mandrel on the surface of which the formed strip is wound. The prior art teaches that the mandrel can be stationary or rotating in order to facilitate the extraction of the pipe from the mandrel as shown in U.S. Pat. No. 1,004,644, U.K. Pat. No. 691,715 and French Patent No. 985,067.
The known rotating apparatuses include, on the same side of the plate where the product is formed, a support for a supply reel of flat strip, an assembly of driven shaping rollers to drive the strip and to give it the required shaped cross-section, guiding means for the strip between the supply reel and the assembly of forming rollers, a tubular mandrel mounted coaxially with the plate, and a forming and extraction mechanism for the winding of the strip onto the mandrel and the longitudinal removal of the pipe formed, downstream of the turning plate, to withdraw the structure formed toward a receiving reel. In addition to the fact that it is not possible with the prior art apparatuses to form an interlocked wound tubular pipe in long lengths without stopping the machine to change the supply reel, significant disadvantages of the prior art apparatuses also arise from the impossibility of controlling the speed of interlocking on the mandrel and the feeding speed of the forming rollers. As a matter of fact, in the prior art this problem is mentioned many times, but no final solution has yet been found.